The static pressure resulting after cessation of flow is thought to reflect the filling of the cardiovascular system. In the past, static filling pressures or mean circulatory filling pressures have only been reported in experimental animals and in human corpses, respectively. We have now investigated arterial and central venous pressures in supine anesthetized humans with longer fibrillation / defibrillation-sequences (FDSs) during cardioverter / defibrillator implantation. In 82 patients, the average number of FDS was 4±2 (mean±SD), and their duration was 13±2 s. In a total of 323 FDSs, arterial blood pressure decreased with a time constant of t = 2.9±1.0 s from 77.5±34.4 mmHg to 24.2±5.3 mmHg. Central venous pressure increased with a time constant of t = 3.6±1.3 s from 7.5±5.2 mmHg to 11.0±5.4 mmHg (36 pts; 141 FDS). The average arterio-central venous blood pressure difference remained at 13.2±6.2 mmHg. Although slowly decreasing, a pressure difference persisted even with FDSs lasting 20 s. Lack of true equilibrium pressure could possibly be due to a waterfall mechanism. However, waterfalls were neither identified between the left ventricle and the arterial system nor at the level of the diaphragm in supine patients. We therefore suggest that static filling pressures / mean circulatory pressures can only be directly assessed, if the time after termination of cardiac pumping is adequate, i.e. > 20 s. For man, such times are beyond ethical options.